Solid propellant pressurizing device



Feb. 12, 1963 K. c. JONES SOLID PROPELLANT PRESSURIZING DEVICE NN m:

NZ?, NO. Nm Q AN \v\ Il AN AN m l n 87V Q d'll'?? Patented Feb. l2, 1953 hice 3,677,677 59MB PRPELLANT PRESSUREZNG DEVltE Keith tC. lonas, Minneapolis, Minn, assigner to Minneap= olie-Honeywell Regulator Company, Minneapolis, Minn., a corporation ol Delaware Filed luly ll, 1959, Ser. No. $24,323 6 Claims. (Cl. till- 39.470

This invention relates to pyrotechnic accumulatore wherein hot gas is generated and used to pressurize a stored quantity of hydraulic fluid, and more particularly, to a hot gas generator wherein the gas is developed by the regulated burning of a quantity of solid propellant over a predetermined period of time so as to maintain pressure on said hydraulic iluid throughout said time interval.

Pyrotechnic auxiliary power units using either liquid or solid fuels have been in existence for some time, and are well known in the art. These units have been, for the most part, designed around a high-speed turbine, driving an alternator and/or hydraulic pump through one or more stages of gear reduction, and the resultant cornpiexity, weight, size and relatively high cost make this type of power unit undesirable for many applications. Another problem in this type of device is that of inhibiting the solid propellant so that it burns at one end-surface only, since the gas production rate cannot be controlled unless the area of the burning surface is controlled. This latter problem becomes particularly acute when the design pressure for the device is in the order of 3,600 pounds per square inch, since high pressures tend to increase the tendency of the fuel to instantly ignite on all surfaces and, essentially, explode. Consideration of these problems in the past has, for the most part, led to the use of a separate gas generator and a separate gas-tohydraulic pressure converter, and this type of construction has further increased the complexity, weight, size and cost as mentioned above.

It is therefore a principal object of my invention to provide a simple and compact device containing hydraulic :duid and solid fuel, wherein said fluid is highly pressurized over a predetermined time interval by gases generated through controlled burning of said fuel.

A further object of my invention is to provide such a device in a relatively small and compact design, having relatively light weight, and being relatively low in cost.

A further object of my invention is to provide such a device wherein a novel structure and method is employed to inhibit the burning of said fuel.

These and other objects of my invention will become apparent upon consideration of the following description, taken in conjunction with the accompanying single sheet of drawing wherein:

FIGURE l is a sectional View of. the hot gas generator forming my invention,

FIGURE 2 is an enlarge sectional view of the ignitor assembly used to ignite the solid fuel, and

FlGURE 3 is an exploded isometric view of my solid propellant assembly.

General Description My hot gas generator is made operative by ignition taking place in the ignition assembly shown in FIGURE 2. This is initated by at least one of two squibs lill and lill, that are normally connected in parallel. These squibs ignite a booster charge of fast burning smokeless powder lili. The ignition charge is contained long enough to build up to a pressure which insures a fast ignition burn. When the necessary elevated pressure is reached, a diaphragm 97 ruptures and releases the burning ignition gases through the ports 96' and across the face of the solid propellant 53. After the solid propellaut is ignited, it supplies hot gases at three thousand pounds per square inch pressure behind a piston 6l (FlG- URE l) which forces hydraulic oil in chamber 6b out of the device at the required flow rate. Exhaust gases also pass around the solid propellant assembly and down its full length by way of longitudinal grooves 56 (see FIG- URE 3) and are then exhausted through a relief valve 4t) (FlGURE l). This relief valve dumps all excess exhaust gases not required by the hydraulic demand, and regulates the three thousand pound per square inch operating pressure. The details of this operation will be best understood from the following more complete description.

Detailed Description In FIGURE l, it is apparent that the main structural member is a body, or internal housing 22. This member has the form of a cylindrical tube provided with male threads at both ends, an outwardly extending circular flange Sil, a plurality of ports 7h', arranged. about a circular groove e9 formed in the inner wall of housing 22, and an inwardly extending circular ilange d'7. An annular gap or chamber, 6h, for hydraulic iluid is formed by a pair of annular end closure members 71 and 23, the outer wall of body 22, and the inner wall of an outer housing member 35. Member 35 is concentrically located around body 22, and tits snugly against a shoulder '72 of end closure member' 7l, and a shoulder 26 of end closure member 23. The components making up this hydraulic chamber are held in fixed relation by a lock nut ll, which threads onto body 22 and compresses elements Z3, 35, and 7l against shoulder 3l) of body Z2. It should be noted that Q-ring seals 2d, 25, 73 and 74 are provided to prevent hydraulic and gas leaks between these members, and that a safety valve i5- 76 is provided in member 7l.

A free-heating ring-type piston el is located in chamber 6i?, and is shown in its normal position at the right end of the chamber. Piston 6l rits snugly against the inner wall of member 35 and tre outer wall of member 22, and is designed to move toward end-closure member 23 under the induence of pressurized gas impinging on its right face. (1i-ring seals 64 and 65 are provided to prevent leakage between the surfaces, and a plurality of pressure balance rings 63 are provided to minimize locking of the pistou in chamber oil and thereby impart greater lubricity to piston movement. It should be noted that a male llange 62 on piston nl is designed to engage a female opening 3d in end-closure member 23, so that all of the hydraulic fluid in chamber et? can be exhausted except that remaining in a fluid line 3l and a port 32 threaded at 33.

In addition to holding the hydraulic chamber components in fixed relation, loclt nut lll is also efectivo to support a portion of the pressure regulating assembly of my device. This pressure regulating assembly includes an inner porting nut 13 having ports le therein, a set screw l5 which threads into nut 13, a spring retainer Zd, a spring 2l, a spring seat 3d, and a valve dll. Valve ell includes a pivot dll, a spool 45, and a sleeve il which is provided with ports such as ft2 and e3. Valve S6 also has male threads ed which engage female threads in flange 47. The compression of spring 2l, and therefore the relief pressure of the assembly, is established by set screw l which can be turned by means of a tool (not shown) inserted through opening l2 in lock nut ll. When suiicient pressure has been generated in the system, gas is ported through sleeve 4l from the right (in a manner to be described below), and against the right end face of spool d5, forcing the spool 455 and pivot le to the left so as to compress spring 2l. Gas is thereby released through ports 42 and 43 in sleeve 4l, ports le in porting nut 13, and through a center opening l2 in hydraulic lock nut ll.

The solid propellant fuel assembly is located tothe right of llange 47, within body 22. An insulator washer is mounted at the left end thereof, and a gas porting end spacer 5l provides a path for gas to flow into sleeve The propellant assembly will be more clearly understood by reference to FlGUP-,E 3, where it is shown in greater detail. This assembly consists a solid propellant stick 53, and a tube :lo housing an end closure 52 and consisting of an epoxy material reinforced with fiberglass, which serves the dual function of housing the propellant stick and also providing a support member for a bonding layer 53 of polyurethane which is injected and cured under pressure between tube Se and propellant stick 53. A steel sleeve 55, with splined grooves 55 therein, holds the liberglass and propellant potted assembly in position, and also provides porting passages to the relief valve. Although grooves Se are shown, it should be understood that a number of diierent types of depressions would be equally effective to port the exhaust gas to the valve. Another steel sleeve 57', having thread-like grooves out in its outside diameter, lits concentrically between sleeve and the inside of body Z2. Sleeve S7 provides the necessary heat insulation due to the dead air space in the grooves and the minimum contact with housing 22, to protect th hydraulic accumulator from the temperature or the hot gases owing around the propellant assembly.

At the right end of propellant stick 53, l have provided a propellant cap 4?, which lits snugly around tube between sleeve 55 and an insulator washer 92. Cap fits against the right end of tube and covers the end of the polyurethane between propellant 53 and sleeve 5d, to protect the sleeve and the bonding layer from the hot gases generated as the propellant 53 burns. Flanges S5 on cap tid act as spacers, and permit the combustion gases to how to the piston and pressure-regulation mechanism. A shield 32 fits snugly into housing 22, and between sleeve 57 and insulator washer 92 and has ports d3 that are aligned with groove oil in housing 2.2. The inside diameter of shield S2 is greater than the outside diameter of propellant cap 8d, and the annular opening therebetween carries the combustion gases to the right end of spline-:l grooves 56 in sleeve 55.

The solid propellant stick or body was potted as shown, in order to obtain end-burning thereof. End-burning was chosen as the means for prescribing and maintaining constant burn area on the solid propellant, and this makes it necessary to coat the sides and bottom of the solid propellant with a burn inhibiting potting material. A virtually air tight, tough, resilient inhibition coating was necessary, clue to the explosive nature of the propellant and the resulting tendency of the burn area to expand into the slightest opening in the potting material. The problem was aggravated by the tendency of the propellant materials to resist adhesion due to the oils and residual solvents contained therein, by the tendoney ot certain potting materials to shrink as they cure, and by the extremely high coeflicient of expansion of the propellant materials. This expansion characteristic made it impossible to use a potting material requiring elevated temperature cure, or an exothermic potting material such as epoxy resin, since the heat would cause the inhibitor to onto an expanded propellant stick, and the stick would then shrink away from the inhibitor as it cooled. lt is also essential to choose a compatible potting material, that is, one that does not include components aiiectcd by or having an adverse effect on the solid propellant material.

I have found it possible to solve these problems by using a thermo-setting material with good adhesion characteristics, such as one of the class of compounds known as polyurethanes. One such material found suitable for the purpose is a urethane manufactured by the Coast Froseal Mfg. Co. and marketed under code number XWC45-4L The material is drawn into the space between stick 53 and tube 54 with a minimum of 4 millimeters of mercury vacuum, and is then slowly cured at room temperature, approximately 70 degrees Farenheit, while rigor? being subjected to 29S pounds per square inch pressure, for a minimum of sixteen hours. The pressure is an essential step in the process, since it forces the polyurethane against the propellant and into the pores therein, which compensates for slight dimensional changes in the stick caused by temperature change. The resultant inhibitor has been found to adhere well to the propellant stick and form a cohesive layer between the stick and the sleeve, this layer having suliicient strength and resilience to maintain the desired end-burning of the propellant.

lgnitor assembly 99 consists of a header 93 which is provided with female threads at the left end thereof to receive a nut 95, perforations 96 being provided therein. Nut and header 93 deiine an internal chamber, or ignition cavity, llltl, which is filled with a fast-burning smokeless powder, a pair of electrically tired squibs N1 and 162 being also mounted therein as shown. The smokeless powder is held in this chamber by a plastic membrane 97 glued to the inside of nut 95 as shown. A seal is provided between body 22 and header @3 by 0- ring 94, and header 93 is held against the end of body Z2 by lock nut 115, which is provided with female threads to engage the male threads cll on the right end of body 22.

Positive ignition is achieved by the use of two squibs, lill. and N2, each of which contains a small charge, and by the booster charge in chamber llltl. The two squibs are identical, and are connected in parallel, to provide ignition redundancy in case one of them should fail to ignite. Each squib consists of a small charge encased in a cardboard cover, this small charge being ignited responsive to an electric current Flowing through a small resistance-wire larnent mounted therein (not shown). Upon receipt of an appropriate electrical signal, the squibs lire and ignite the booster charge of smokeless powder, to thereby raise the pressure in the ignition cavity ltlll. After the pressure has risen to approximately 1000 pounds per square inch, the membrane 97 ruptures, allowing the gases to expand from the ignition cavity through perforations h6 in perforated nut 95 onto the end of propellant stick 53. The expansion or the gases from the ignition cavity to the face of the stick is restricted by the pressure drop through holes 96 in perforated disc 95 of ignition cavity lill), thus maintaining the elevated pressure within the ignition cavity and allowing the continuation of fast burn of the remainder of the smokeless powder. This permits fast and positive burning of the ignition charge, and assures positive ignition of the propellant stick. The energizing leads for squibs lill and 162 are schematically shown as leads and lilo, encased in a tubing llld extending to squib lill, and leads lll and 1212 are encased in a tubing il?) which extends to squib 162. Plugs w3 and ll@ are iirmly mounted in header 93, and provide a positive seal around the lead wires and tubes idd and 3113, to prevent the escape of gas therearound.

Operation When squibs lill and ltlZ are tired, and powder lo@ is ignited, the adjacent end of propellant stick 53 is also ignited and begins to burn from the end in much the same manner as a cigarette, although considerably faster. The burning rate is determined by the propellant material that is used, and the area of burn is determined by the outer casing and potting that is used to contain the propellant stick, as described above. For this application, I have sized the propellant stick, and chosen a propellant, to provide a pressure versus burn-rate curve that has a somewhat iattened plateau range close to the desired operating pressure of 3000 pounds per square inch. This permits a closer maintenance of a desired operating pressure, without the necessity of exhausting large variations in quantities or" gas through the regulating valve assembly.

As the pressure builds up, the gases llow between flanges 85 on cap 8d, into the annular groove between cap @d and shield 82, through ports S3 to groove 69, through ports 7), and between end closure member 7l and piston '61. Piston 61 is thereby forced to the left, against the hydraulic liuid in chamber 60. Suliicient propellant is provided to maintain the operating pressure of 3,000 pounds per square inch behind piston 61 until all of the lluid has been exhausted from chamber 60, and shoulder 62 is seated in groove 30. Thus, hydraulic fluid is forced into groove 30, and through fluid line 31, and from there out of port 33 to the operated device. "the propellant is sized to burn in approximately five seconds, but when hydraulic fluid is not being used, pressure will remain at the operating value of 3,000 pounds per square inch for an additional one to two seconds before the temperature of the gas drops to a value below that required for maintenance of operating pressure.

There is considerable diliculty in predicting the precise burning rate of the solid propellant, and even greater difficulty in anticipating the rate at which hydraulic fluid will be used, and it therefore becomes necessary to provide la pressure relief mechanism to prevent a build-up of pressure that could possibly destroy the overall device. Thus, when pressure builds up due to the burning of propellant stick 53, some of the gases ilow from the annular space between elements 82 and 84, into longitudinal grooves 56, between spacer :31 and insulator Washer 50, through Washer 50 and sleeve 4d, and against the right hand face of spool 45, as viewed in FIGURE 1. When the pressure on spool 45, which is equal to the hydraulic pressure in chamber 6i), exceeds the predetermined maximum setting of the valve, spool 45 moves to the left. This permits gas to new through ports 42 `and 43, and from there through ports 14 and 12 to be exhausted from the device.

What has been described is considered to be the preerred embodiment of my invention. However, it should be understood that various changes and modifications thereof may be made without departing from the spirit and `scope or" the invention, as defined in the appended claims.

What is claimed is:

1. in combination: =a propellant stick including an elongated charge of pyroteuhnical material, a housing therefor of heat insulating material open at one end, and combustion inhibiting bonding means joining said charge to said housing in flexible, air tight relation to prevent lany combustion of said charge except end-burning at the end thereof nearest the open end of said housing; an elongated firying chamber, having a body and end closures, for receiving said stick; gas pressure regulating means associated with one of said end closures; ignition means associated with the other of said end closures, adjacent to the end of said stick at which said end-burning is to take place; and sleeve means between said stick and the body of said chamber and formed to provide passage for gas between the ends of said chamber.

2. In combination: an elongated firing chamber having open ends and a wall with gas conducting channel means passing laterally therethrough; a first end closure for said chamber including gas pressure regulating means; a second end closure for said chamber including inwardly directed combustion initiating means; chamber lining means inoluding an end portion next to said first end closure and a tubular portion extending therefrom towards said second end closure and having lateral passage means extending therethrough and positioned for alignment with said channel means in said chamber; a solid propellant stick substantially filling said lining means and positioned for ignition by said combustion initiating means to produce gas by end-burning at the end nearest thereto; `and means including said lining means providing a passage for gas be tween said end closures.

3. In combination: an elongated firing chamber having a wall and open ends; a rst end closure for said chamber including gas pressure regulating means; a second end end closure for said chamber including inwardly directed combustion initiating means; chamber lining means including an end portion next to said first end closure and a `tubular portion extending therefrom towards said second end closure; a solid propellant stick substantially filling said lining means and positioned for ignition by said combustion initiating means to produce gas by end-burning at the end nearest thereto; and means including said lining means providing a passage for gas between said end closures.

4. In a pyrotechnic accumulator, in combination: a tiring chamber adapted to receive an elongated propellant stick and comprising an open end, a closed end, and an elongated barrel having gas conducting channel means passing outwardly therethrough near said open end; gas pressure regulating means in said closed end; an end closure for said open end including inwardly acting combustion-initiating means; a first, heat insulating liner within said barrel including end portions apertured for cooperation with said pressure regulating means and said combustion initiating means, and a tubular intermediate portion apertured for cooperation with said channel means; and a second liner having internal dimensions substantially the same as the external dimensions of said propellant stick, said liners being formed to cooperate for providing passage means for gas from end to end of said chamber, said passage means communicating with the apertures in said first liner.

5. In a pyrotechnic accumulator, in combination: a tiring chamber adapted to receive an elongated propellant stick and comprising an open end, a closed end, and an elongated barrel having gas conducting channel means passing outwardly therethrough near said open end; gas pressure regulating means in said closed end; an end closure for said open end including inwardly acting combustion-initiating means; lining means within said barrel having internal dimensions substantially the same as the external dimensions oi said stick, and external dimensions substantially the same as the internal dimensions of said barrel; and passage means defined by said lining means for conducting gas between the ends of said chamber, said passage means communicating with the apertures in said first liner.

6. In a pyrotechnic accumulator, in combination: a firing chamber adapted to receive an elongated propellant rstick and comprising an open end, a closed end, and an elongated barrel; gas pressure regulating means in said closed end; end closure for said opening end including inwardly acting combustion initiating means; a first, heat insulating liner within said barrel including end portions, apertured for cooperation with said pressure regulating means and said combustion initiating means, and a tubular intermediate portion; `and a second liner having internal dimensions substantially the same as the external dimensions of said propellant stick, said liner being formed to cooperate for providing passage means for gas from end to end of said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,935,123 Lansing Nov. 14, 1933 2,154,572 Lansing Apr. 18, 1939 2,539,404 Crutchfield et al Ian. 30, 1951 2,544,422 Goddard Mar. 6, 1951 2,620,627 Nardone Dec. 9, 1952 2,671,312 Roy Mar. 9, 1954 2,744,043 Ramberg May 1, 1956 2,818,914 Thomann et al. Ian. 7, 1958 2,865,456 Dennis Dec. 23, 1958 2,877,504 Fox Mar. 17, 1959 2,942,547 Rabern et al lune 28, 1960 2,952,972 Kimmel et al. Sept. 20, 1960 `2,957,309 Kobbeman Oct. 25, 1960 2,977,879 Rice Apr. 4, 1961 2,989,844 Alden June 27, 1961 2,990,684 Cohen Iuly 4, 1961 

1. IN COMBINATION: A PROPELLANT STICK INCLUDING AN ELONGATED CHARGE OF PYROTEUHNICAL MATERIAL, A HOUSING THEREFOR OF HEAT INSULATING MATERIAL OPEN AT ONE END, AND COMBUSTION INHIBITING BONDING MEANS JOINING SAID CHARGE TO SAID HOUSING IN FLEXIBLE, AIR TIGHT RELATION TO PREVENT ANY COMBUSTION OF SAID CHARGE EXCEPT END-BURNING AT THE END THEREOF NEAREST THE OPEN END OF SAID HOUSING; AN ELONGATED FIRING CHAMBER, HAVING A BODY AND END CLOSURES, FOR RECEIVING SAID STICK; GAS PRESSURE REGULATING MEANS ASSOCIATED WITH ONE OF SAID END CLOSURES; IGNITION MEANS ASSOCIATED WITH THE OTHER OF SAID END CLOSURES, ADJACENT TO THE END OF SAID STICK AT WHICH SAID END-BURNING IS TO TAKE PLACE; AND SLEEVE MEANS BETWEEN SAID STICK AND THE BODY OF SAID CHAMBER AND FORMED TO PROVIDE PASSAGE FOR GAS BETWEEN THE ENDS OF SAID CHAMBER. 